1. Field
The present disclosure relates to a method and a system for calibrating an image printing system that includes a plurality of parallel printers.
2. Description of Related Art
Generally, the black point compensation (BPC) function is used for RGB images to retain shadow details in images because many images contain colors that are darker than the darkest color a printer can make. Without black point compensation, details in these shadow regions may be lost. These details may contain information the viewer knows should be there (such as, for example, the folds of a dark coat, the strands of dark hair, etc). Their absence when printed may be displeasing for a particular user.
The black point compensation may include an input L* (input image data) to output L* (image data to be rendered by the printer) mapping function that is used in the color management look-up table (LUT). This input L* to output L* mapping function is a parameterized quadratic or parabolic function which is used to modify the L* values of all the node colors in the multi-dimensional look up table. The black point compensation is used as a single-valued scalar function.
The black point compensation function that retains the details in dark colors (e.g., hairs) includes two parameters: minimum luminance value, L*min and slope, m. These two parameters (i.e., L*min and m) are used to control the effects (i.e., retain darkness vs details) in images. Digital production color printers, such as the Xerox Corp. DocuColor™ 5000 and 8000 Digital Presses, may show excessive gloss levels in color prints particularly when images with dark shadow colors are printed. In case of these digital production color printers, a gloss control slider at a graphical user interface (GUI) may also be linked to adjust these two parameters (i.e., L*min and slope) to provide compensation for excessive amount of gloss levels in color prints or images.
In a tightly integrated parallel printing (TIPP) configuration, the minimum luminance value L*min for each of the printers may be different. For example, the minimum luminance value L*min for the image printing system may vary from 10 to 15 from one printer to another printer. By using these different minimum luminance values L*min in the existing black point compensation function may result in a mismatch in RGB images, particularly in shadow details.
The present disclosure proposes to extend the existing black point compensation to a TIPP configuration such that the shadow details and the gloss levels from the two printers will match.